Fair enough. The reason I ask is because you will see many of the people who have been doing this a long time recommend against building an 808 or 909 in a rack due to both cost and workflow. This is good advice. When it comes to performing techno, it's really hard to argue against an external X0X sequencer. In my opinion it's the best option. Everything is already hardwired but still tweakable, and you can still integrate it with your rack via the clock, triggers, and individual outs.
I have taken this hybrid approach myself. I use a combination of the Behringer RD8 (the only Behringer piece I own, but I love it) and some Eurorack drums and multiple Euro sequencers. I initially tried to do what you are planning but found that the performance workflow was severely limited. Building around an external drum machine really encouraged a hands-on approach. There are a few mind-blowing YouTube videos of Jeff Mills performing techno on an old TR909. Check them out. Some people like Elektron drum machines but I never gelled with their ergonomics. You won't have CV control over every parameter of the 909 sounds, but you can add things like Basimilus and WMD drum modules (or oscillators and LPGs) to your rack as a supplement so you have control over other drum sounds.
If you are just getting started building this, allow yourself some room to change direction with your build. You may find that what you think you would enjoy workflow-wise is really awful. Take your time and only add a module or two at a time.
-- farkas
I really appreciate the advice and it's definitely something to keep in mind. I do plan on only adding a couple modules at a time as I don't have thousands of dollars to spend at a moments notice, and the drums/sequencer were (maybe are) definitely going to be bought last in case I change my mind. Thank you!